Wired circuit board and production method thereof

ABSTRACT

A wired circuit board that can provide improved reliability on connection between the terminal portions and the external terminals while ensuring high productivity and cost reduction, and a production method thereof. After a conductive pattern  3  including terminal portions  6  to connect with external terminals  22  of an electronic component  21  and criterion marks  8  to determine presence or absence of an inhibitory portion  23  that may be formed due to formation of an insulating cover layer  4  to inhibit connection between the terminal portions  6  and the external terminals  22  are formed on the insulating base layer  2  simultaneously, the insulating cover layer  4  to cover the conductive pattern  3  and an opening  7  from which the terminal portions  6  and the criterion marks  8  are exposed is formed. Thereafter, the presence or absence of the inhibitory portion  23  is determined with reference to the criterion marks  8  exposed from the opening  7  of the insulating cover layer  4.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 11/349,188 filed Feb. 8, 2006, now U.S. Pat. No.7,371,971 which claims priority from Japanese Patent Application No.2005-33327, filed on Feb. 9, 2005, the contents of which are hereinincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wired circuit board and to aproducing method thereof. More particularly, the present inventionrelates to a wired circuit board having a terminal portion to beconnected with external terminals and to a producing method thereof.

2. Description of the Prior Art

The wired circuit board usually has a conductive pattern configured by aplurality of lines of wire formed on an insulating base layer andfurther has an insulating cover layer formed on the insulating baselayer to cover the conductive pattern.

This wired circuit board has a terminal portion formed in the conductivepattern to be connected with external terminals of an electroniccomponent and the like. The insulating cover layer is formed to have anopening formed to correspond to the terminal portion so that theterminal portion can be exposed from the opening to connect with theexternal terminals.

Accordingly, positional precision of the relative position of theterminal portion with the opening and dimensional precision of theopening are critical for connecting the terminal portion with theexternal terminals with high precision.

There are three known methods for forming the insulating cover layer tohave the opening in it, as outlined below. The first method is a methodusing a screen printing method in which a solder resist is formed toform the opening in the insulating cover layer. The second method is amethod in which an insulating resin film with a preformed opening isadhesively bonded to form the opening in the insulating cover layer, ora method in which an insulating resin film is adhesively bonded, first,and, then, the opening is formed in the insulating resin film. The thirdmethod is a method using photolithography in which after coated,photosensitive resin is exposed to light and developed to form theopening in the insulating cover layer.

However, the first method has the problem that when printed (coated),solder resist 30 may flow into between lines of wire 34 at the terminalportions 33 exposed from the opening 32 of the insulating cover layer 31due to the capillary phenomenon until it reaches an electronic componentmounting place 35 where the terminal portion 33 is connected with theexternal terminals, as shown in FIG. 14. In this case, it becomesdifficult to mount the electronic component to connect the externalterminals with the terminal portion 33.

The second method has the problem that an adhesive may flow into betweenthe lines of wire 34 due to the capillary phenomenon until it reachesthe electronic component mounting place 35 where the terminal portion 33is connected with the external terminals, as is the case with the firstmethod. In this case also, it becomes difficult to mount the electroniccomponent to connect the external terminals with the terminal portion33.

The third method has the problem that when a photo mask is out ofposition in the process of the photolithography, the electroniccomponent mounting position 35 may be covered with the insulating coverlayer 31, as shown in FIG. 15. In this case also, it becomes difficultto mount the electronic component to connect the external terminals withthe terminal portion 33.

The prior art proposes a solution that the lines of wire at the terminalportion are machined using a bending or pressing process to provide e.g.an indented surface to make it hard for the solder resist to flow out,so as to prevent the solder resist printed from flowing out to a devicehole side (Cf. JP Laid open (Unexamined) Patent Publication No.2003-309148, for example).

However, the provision of the indented surface for the line of wire bythe machining process requires a cumbersome and complicated work,causing reduction in workability and increase in cost.

Also, it is usual that whether or not the insulating cover layer reachesthe electronic component mounting place is determined by a continuitytest after the mounting of the electronic component or by measurement ofa dimension of the insulating cover layer flown in between the lines ofwire at the terminal portions. However, such an inspection carried outduring the production process makes it hard to provide cost reductionwhile ensuring high productivity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wired circuitboard that can provide improved reliability on connection between theterminal portions and the external terminals while ensuring highproductivity and cost reduction, and a production method thereof.

The present invention provides a novel wired circuit board comprising aninsulating base layer, a conductive pattern formed on the insulatingbase layer, and an insulating cover layer formed on the insulating baselayer to cover the conductive pattern, wherein the conductive patternincludes terminal portions to connect with external terminals, whereinan opening is formed in the insulating cover layer to correspond to theterminal portions, and wherein criterion marks are provided at thelocations adjacent to the terminal portions on the insulating base layerexposed from the opening, to determine presence or absence of aninhibitory portion that may be formed due to formation of the insulatingcover layer to inhibit connection between the terminal portions and theexternal terminals.

Also, the present invention provides a novel production method of awired circuit board comprising the process of forming a conductivepattern including terminal portions to connect with external terminalson an insulating base layer, the process of forming an insulating coverlayer on the insulating base layer to cover the conductive pattern andform an opening from which the terminal portions are exposed, and theprocess of determining presence or absence of an inhibitory portion thatmay be formed due to formation of the insulating cover layer to inhibitconnection between the terminal portions and the external terminals,wherein in the process of forming the conductive pattern, criterionmarks to determine presence or absence of the insulating cover layerthat may inhibit connection between the terminal portions and theexternal terminals are formed on the insulating base layer exposed fromthe opening at the same time as the conductive pattern is formed, andwherein in the process of determining the presence or absence of theinhibitory portion that may be formed due to the formation of theinsulating cover layer to inhibit the connection between the terminalportions and the external terminals, the presence or absence of theinhibitory portion is determined with reference to the criterion marks.

In the wired circuit board of the present invention, the criterion marksto determine the presence or absence of the inhibitory portion that maybe formed due to the formation of the insulating cover layer to inhibitthe connection between the terminal portions and the external terminalsare formed at locations adjacent to the terminal portions on theinsulating base layer exposed from the opening. This can facilitatedetermination on whether the inhibitory portion is present or absent,using the criterion marks as the basis for the determination. This canprovide a wired circuit board that can provide improved reliability onconnection between the terminal portions and the external terminalswhile ensuring high productivity and cost reduction.

In the production method of wired circuit board of the presentinvention, the criterion marks and the conductive pattern are formedsimultaneously for determining the presence or absence of the inhibitoryportion that may be formed due to the formation of the insulating coverlayer to inhibit the connection between the terminal portions and theexternal terminals, using the criterion marks as the basis for thedetermination. This method can allow effective formation of thecriterion marks and can facilitate determination on whether theinhibitory portion is present or absent, using the criterion marks asthe basis for the determination. This can provide the result ofproviding improved reliability on the connection between the terminalportions and the external terminals while ensuring high productivity andcost reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1( a) is a sectional view of a principal part of a wired circuitboard of an embodiment of the present invention, and FIG. 1( b) is aplan view of a principal part of the wired circuit board shown in FIG.1( a),

FIG. 2 is a production process drawing showing a production method ofthe wired circuit board shown in FIG. 1,

(a) showing the process of preparing an insulating base layer,

(b) showing the process of forming a conductive pattern and a criterionmark simultaneously on the insulating base layer,

(c) showing the process of forming an insulating cover layer on theinsulating base layer to form an opening from which a terminal portionis exposed, and

(d) showing the process of forming a metal plating layer on the lines ofwire at the terminal portion exposed from the opening of the insulatingcover layer,

FIG. 3 is an explanatory view of the principal part, illustrating thestate that solder resist flows into between the lines of wire at theterminal portions to form an inhibitory portion, which is determinedwith reference to the criterion marks,

FIG. 4 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (generallyL-shaped criterion marks, as viewed from top, spaced apart from thelines of wire),

FIG. 5 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (generallysquare criterion marks, as viewed from top, spaced apart from the linesof wire),

FIG. 6 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (generallysquare criterion marks, as viewed from top, located between the lines ofwire),

FIG. 7 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (triangularcriterion marks, as viewed from top, spaced apart from the lines ofwire),

FIG. 8 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (cruciformcriterion marks, as viewed from top, spaced apart from the lines ofwire),

FIG. 9 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (criterionmarks of numeric character 1, as viewed from top, spaced apart from thelines of wire),

FIG. 10 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (T-shapedcriterion marks, as viewed from top, spaced apart from the lines of wireand extending along a lengthwise direction of the wired circuit board),

FIG. 11 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (T-shapedcriterion marks, as viewed from top, spaced apart from the lines of wireand extending along a widthwise direction of the wired circuit board),

FIG. 12 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (L-shapedcriterion marks, as viewed from top, spaced apart from the lines ofwire),

FIG. 13 is an explanatory view of the principal part corresponding toFIG. 3, showing another embodiment of the criterion marks (circularcriterion marks, as viewed from top, spaced apart from the lines ofwire),

FIG. 14 is an explanatory view of a principal part of a conventionalconductive pattern corresponding to FIG. 3 (an aspect of the insulatingcover layer formed by the solder resist), and

FIG. 15 is an explanatory view of a principal part of a conventionalconductive pattern corresponding to FIG. 3 (an aspect of the insulatingcover layer formed by the photolithography using a photosensitiveresin).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1( a) is a sectional view of a principal part of a wired circuitboard of an embodiment of the present invention, and FIG. 1( b) is aplan view of a principal part of the wired circuit board shown in FIG.1( a).

In FIG. 1, the wired circuit board 1 is a flexible wired circuit boardextending like a generally square strip as viewed from top, comprisingan insulating base layer 2, a conductive pattern 3 formed on theinsulating base layer 2, and an insulating cover layer 4 formed on theinsulating base layer 2 to cover the conductive pattern 3, as shown inFIG. 1( a).

The insulating base layer 2 is formed in a generally rectangular stripform as viewed from top, as shown in FIG. 1( b).

The conductive pattern 3 is configured by a plurality of lines of wire 5extending along a lengthwise direction of the wired circuit board 1 andarranged in parallel with each other at spaced intervals in a widthwisedirection of the wired circuit board 1 (a direction orthogonal to thelengthwise direction of the wired circuit board 1), including terminalportions 6 to connect with external terminals 22 of an electroniccomponent 21. The terminal portions 6 are formed so that the lines ofwire 5 are divided at spaced intervals in the lengthwise direction ofthe wired circuit board 1. A width W1 of each line of wire 5 is set tobe in the range of 5-500 μm, and an interval W2 between adjacent linesof wire 5 is set to be in the range of 5-500 μm. When the interval W2between the lines of wire 5 is not more than 5 μm, it comes to be likelythat an inhibitory portion 23 mentioned later (Cf. FIG. 3) is formedbetween those lines of wire.

An opening 7, opened in a generally rectangular form as viewed from top,is formed in the insulating cover layer 4 to confront the terminalportions 6 with respect to a laminating direction of the respectivelayers being laminated and also surround the terminal portions 6.

In this wired circuit board 1, criterion marks 8 are provided on theinsulating base layer 2 exposed from the opening 7 of the insulatingcover layer 4 at the locations adjacent to the terminal portions 6.

The criterion marks 8 are formed to determine the presence or absence ofan inhibitory portion 23 that may be formed due to formation of theinsulating cover layer 4, as mentioned later, to inhibit the connectionbetween the terminal portions 6 and the external terminals 22 of theelectronic component 21 (Cf. FIG. 3).

The criterion marks 8 are provided on the lines of wire 5 at both endsthereof in the widthwise direction, one on each side of four opposinglines of wire 5 at the terminal portions 6 divided in the lengthwisedirection of the wired circuit board 1 (four in total).

The criterion marks 8 are in the form of a square, as viewed from top,and are arranged to contact with the lines of wire 5 located atwidthwise outermost sides of the terminal portions 6 from widthwiseoutside.

A lengthwise dimension L1 of each criterion mark 8 is set to be in therange of 15-150 μm, or preferably 30-80 μm, and a widthwise dimension ofthe same is set to be in the range of 15-150 μm, or preferably 30-80 μm.If the criterion marks 8 have larger dimensions, then available spacesfor the criterion marks 8 to be provided will be limited. On the otherhand, if the criterion marks 8 have smaller dimensions, then it maybecome difficult to observe the criterion marks 8.

Also, the criterion marks 8 are located between a mounting position 24for the external terminals 22 of the electronic component 21 to beconnected with the terminal portions 6 and ends of the opening 7 withrespect to the lengthwise direction of the lines of wire 5 in theterminal portions 6. To be more specific, solder resist or adhesivementioned later may flow into between the lines of wire 5 inwardly tothe opening 7 along the lengthwise direction of the lines of wire 5.When the solder resist or adhesive comes closer to the mounting position24, the electronic component 21 cannot be properly mounted by theinhibitory portion 23 formed by the solder resist or adhesive (Cf. FIG.3). Accordingly, the criterion marks 8 are located in close proximity tothe positions where the connection between the external terminals 22 andthe terminal portions 6 may be inhibited by the inhibitory portion 23.The locations for the criterion marks 8 to be situated are properlydetermined depending on the types of the electronic components 21. Forexample, the criterion marks 8 are spaced e.g. at least 200 μm, orpreferably 220-300 μm, apart from the mounting position 24 in thelengthwise direction of the lines of wire 5 which is the spaced intervalS1 between the mounting position 24 and the criterion marks 8.

The lines of wire 5 at the terminal portions 6 exposed from the opening7 of the insulating cover layer 4 are covered with a metal plating layer9 (shown in FIG. 1( a) only) to ensure the reliability on the connectionwith the external terminals 22 of the electronic component 21.

Next, a production method of this wired circuit board 1 will bedescribed with reference to FIG. 2.

In this method, the insulating base layer 2 is prepared, first, as shownin FIG. 2( a).

The materials that may be used for the insulating base layer 2 include,for example, synthetic resins in film form, such as polyimide resin,polyamide imide resin, acrylic resin, polyether nitrile resin, polyethersulfonic resin, polyethylene terephthalate resin, polyethylenenaphthalate resin and polyvinyl chloride resin. Polyimide resin ispreferably used for the insulating base layer 2.

The insulating base layer 2 is prepared using a synthetic resin film. Itmay be prepared by the method that after a varnish of synthetic resincoated is formed on a stripping sheet, not shown, by a casting method,and dried, and cured, if necessary, or by the method that after thevarnish of photosensitive synthetic resin coated is formed on thestripping sheet, it is dried, exposed to light, and developed, to formthe coating of a predetermined pattern, and cure it, if necessary. Theinsulating base layer 2 thus formed has thickness of e.g. 5-50 μm.

Then, the conductive pattern 3 and criterion marks 8 are simultaneouslyformed on the insulating base layer 2, as shown in FIG. 2( b). Forexample, copper, nickel, gold, solder, or alloys thereof may be used forthe conductive pattern 3 and the criterion marks 8. Copper is preferablyused for them in terms of electrical conductivity, cost efficiency, andeasiness in workability.

The conductive pattern 3 and the criterion marks 8 can be simultaneouslyformed on the insulating base layer 2 by a known patterning process,such as a subtractive process and an additive process. In theseprocesses, the conductive pattern 3 is formed in the form of apredetermined pattern configured by a plurality of lines of wire 5including the terminal portions 6 described above, and the criterionmarks 8 are formed to be continuous with the lines of wire 5 located atwidthwise outermost sides of the terminal portions 6.

Specifically, in the subtractive process, a metal foil is laminated onthe entire surface of the insulating base layer 2 via, if necessary, anadhesive layer, first. Then, etching resist having a correspondingpattern to the conductive pattern 3 and the criterion marks 8 is formedon a surface of the metal foil. The etching resist is formed by a knownprocess using photosensitive dry film resist and the like. Thereafter,after the metal foil exposed from the etching resist is removed byetching, the etching resist is removed by etching or stripping.Alternatively, the conductive pattern 3 and the criterion marks 8 may besimultaneously formed on the insulating base layer 2 by the method thata two-layer base material comprising the metal foil laminated on theinsulating base layer 2 is prepared and, then, the metal foil is removedby etching.

In the additive process, a thin metal film (a seed film) is formed onthe entire surface of the insulating base layer 2, first. The thin metalfilm is formed by a thin film formation process, such as a sputteringprocess, using chromium, nickel, copper, and alloys thereof. Then, aplating resist of a reverse pattern to the conductive pattern 3 andcriterion marks 8 is formed on a surface of the thin metal film. Theplating resist is formed by a known process using a photosensitive dryfilm resist, and the like to be exposed to light and developed.Thereafter, the conductive pattern 3 and the criterion marks 8 aresimultaneously formed on the surface of the insulating base layer 2exposed from the plating resist. The conductive pattern 3 and thecriterion marks 8 are formed by the electrolytic plating, or preferablyby the electrolytic copper plating, for example. Thereafter, the platingresist is removed by etching or stripping and then the thin metal filmexposed from the conductive pattern 3 and the criterion marks 8 isremoved by etching.

As a result, the criterion marks 8 and the conductive pattern 3including the terminal portions 6 are formed simultaneously, as shown inFIG. 1( b). The conductive pattern 3 and the criterion marks 8 havethickness of e.g. 3-50 μm.

Then, the insulating cover layer 4 is formed on the insulating baselayer 2, to form in the insulating cover layer 4 the opening 7 fromwhich the terminal portions 6 are exposed, as shown in FIG. 2( c).

The insulating cover layer 4 is formed so that the opening 7 can beformed in the solder resist by a screen printing method. To be morespecific, after known solder resist of epoxy type, acrylic type,urethane type, or the like type is coated over the insulating base layer2 including the conductive pattern 3, the opening 7 is formed in thesolder resist by the known screen printing method and then the solderresist is cured, thereby forming the insulating cover layer 4.

The insulating cover layer 4 may be formed in such a manner that asynthetic resin film (preferably, polyimide resin film) having theopening 7 previously formed by punching and the like is prepared andthat film is adhesively bonded on to the insulating base layer 2including the conductive pattern 3 via an adhesive or in such analternative manner that after a synthetic resin film (preferably,polyimide resin film) is adhesively bonded on to the insulating baselayer 2 including the conductive pattern 3 via the adhesive, the opening7 is formed in that film by drilling, laser processing, etching, or thelike. The adhesives that may be used include, for example, an epoxy typeof adhesive and an acrylic adhesive. The adhesive layer formed by theadhesive has thickness of e.g. 5-30 μm.

Further, the insulating cover layer 4 may be formed to have the opening7 formed by a known photolithography of exposing the photosensitiveresin to light and developing it. To be more specific, after a varnishof synthetic resin coated is formed on the insulating base layer 2including the conductive pattern 3 by the casting method, and dried.Then, the resulting coating is patterned to form the opening 7 by beingexposed to light through a photo mask, developed, and cured, therebyforming the insulating cover layer 4.

The insulating cover layer 4 thus formed has thickness of e.g. 3-30 μm.

Then, the metal plating layer 9 is formed on the lines of wire 5 at theterminal portions 6 exposed from the opening 7 of the insulating coverlayer 4, as shown in FIG. 1( d). The metals that may be used for themetal plating layer 9 include, for example, gold and nickel. The metalplating layer 9 is formed, for example, by electroless plating orelectrolytic plating. Preferably, a nickel plating layer and a goldplating layer are laminated sequentially. In the case where the metalplating layer 9 is the gold plating layer, the metal plating layer 9 hasthickness of e.g. 0.1-1 μm. In the case where the metal plating layer 9is the nickel plating layer, the metal plating layer 9 has thickness ofe.g. 0.5-5 μm.

Since the criterion marks 8 are formed to be continuous with theconductive pattern 3, the metal plating layer 9, when formed byelectrolytic plating, is formed not only on the conductive pattern 3 butalso on the criterion marks 8 by feeding power from common plating lead.The metal plating layer 9 can prevent corrosion of the criterion marks8.

In this method, the presence or absence of the inhibitory portion 23 isdetermined with reference to the criterion marks 8 exposed from theopening 7 of the insulating cover layer 4, as shown in FIG. 3.

For example when the insulating cover layer 4 is formed from the solderresist, the solder resist, when coated, may flow into between the linesof wire 5 at the terminal portions 6 due to the capillary phenomenon,going inwardly of the opening 7 in the lengthwise direction of the linesof wire 5. When the flowing solder resist goes beyond the criterionmarks 8 or goes across a reference line BL indicated by a dotted lineconnecting between the criterion marks 8 opposing in the widthwisedirection, a portion of the solder resist extending inwardly beyond thecriterion marks 8 is determined as the inhibitory portion 23.

For example when the insulating cover layer 4 is formed from thesynthetic resin film to be adhesively bonded, the adhesive may flow intobetween the lines of wire 5 at the terminal portions 6 due to thecapillary phenomenon when the synthetic resin film is laminted, goinginwardly of the opening 7 in the lengthwise direction of the lines ofwire 5. When the flowing adhesive goes beyond the criterion marks 8 orgoes across the reference line BL indicated by the dotted lineconnecting between the criterion marks 8 opposing in the widthwisedirection, a portion of the adhesive extending inwardly beyond thecriterion marks 8 is determined as the inhibitory portion 23.

For example when the insulating cover layer 4 is formed by thephotolithography using photosensitive resin to be exposed to light anddeveloped, the insulating cover layer 4 formed may be displaced towardthe mounting position 24 with respect to the criterion marks 8 due tothe out-of-position of the photo mask, not shown. A portion of theinsulating cover layer 4 formed and displaced toward the mountingposition 24 with respect to the criterion marks 8 is determined as theinhibitory portion 23.

The presence or absence of the inhibitory portion 23 is determined withreference to the criterion marks 8 by observation under an opticalmicroscope (of e.g. 20-40 magnifications), for example.

When the inhibitory portion 23 is determined as “Present”, the wiredcircuit board 1 having such an inhibitory portion 23 is dealt with asdefective goods which is unfit for mount of the electronic component 21so that the connection between the external terminals 22 and theterminal portions 6 may be inhibited.

On the other hand, when the inhibitory portion 23 is determined as“Absent”, the wired circuit board 1 having such an inhibitory portion 23is dealt with as confirming goods which is fit for use so that the goodconnection between the external terminals 22 and the terminal portions 6can be ensured. In this case, the electronic component 21 can be mountedon the wired circuit board 1 to electrically connect the externalterminals 22 of the electronic component 21 with the lines of wire 5 atthe terminal portions 6, as shown in FIG. 1( a), for example.

In the production method of this wired circuit board 1, the criterionmarks 8 are formed at the same time as the conductive pattern 3 and thepresence or absence of the inhibitory portion 23 is determined withreference to the criterion marks 8. This can allow effective formationof the criterion marks 8 and can facilitate determination on whether theinhibitory portion 23 is present or absent, using the criterion marks 8as the basis for the determination. This can provide the result ofproviding improved reliability on the connection between the lines ofwire 5 at the terminal portions 6 and the external terminals 22 of theelectronic component 21 while ensuring high productivity and costreduction.

In the wired circuit board 1 thus produced, since the determination onwhether the inhibitory portion 23 is present or absent can befacilitated, using the criterion marks 8 as the basis for thedetermination, there can be provided the wired circuit board 1 that canprovide improved reliability on connection between the lines of wire 5at the terminal portions 6 and the external terminals 22 of theelectronic component 21 while ensuring high productivity and costreduction.

While in the illustration above, the criterion marks 8 are formed in asquare form, as viewed from top, to contact with the lines of wire 5located at the widthwise outermost sides of the terminal portions 6, forexample, additional lines of wire 10 used particularly for forming thecriterion marks 8 may be formed at the both widthwise outer sidesfurther away from the both widthwise outermost sides of the lines ofwire 5 at the terminal portions 6 so that they can be provided, at freeend portions thereof, with the criterion marks 8.

In FIG. 4, the additionally arranged lines of wire 10 extend along thelengthwise direction of the wired circuit board 1 and are arrayed inparallel at widthwise spaced intervals from the lines of wire 5 locatedat the widthwise outermost positions. The criterion marks 8 are formedin a generally L-shape to bend inwardly in the widthwise direction fromthe additionally arranged lines of wire 10 to the lines of wire 5located at the widthwise outermost positions respectively, when viewedfrom top. A free end of each criterion mark 8 at its inner side in thewidthwise direction is spaced apart from the related line of wire 5 atthe widthwise outermost side in the widthwise direction.

Since the criterion marks 8 of the wired circuit board 1 shown in FIG. 4are also formed to be continuous with the additionally arranged lines ofwire 10, the metal plating layer 9, when formed by electrolytic plating,can be formed not only on the conductive pattern 3 but also on thecriterion marks 8 by feeding power from common plating lead, to preventcorrosion of the criterion marks 8.

While in the illustration above, the criterion marks 8 are arranged tocontact with the lines of wire 5 located at the widthwise outermostsides of the terminal portions 6, for example, the criterion marks 8 maybe spaced apart from the lines of wire 5 located at both widthwiseoutermost sides of the terminal portions 6 at a spaced interval S2, asshown in FIG. 5. The space S2 at which the criterion marks 8 arewidthwise spaced from the related lines of wire 5 is set to be withine.g. 70 μm, or preferably in the range of 15-30 μm.

Further, the criterion marks 8 may be arranged between the adjacentlines of wire 5 along the widthwise direction, as shown in FIG. 6.

As a substitute for the criterion marks 8 of square as viewed from topshown in FIG. 5, the criterion marks 8 may be formed in any geometricalor alphabetical shape, as viewed from top, such as, for example, atriangular shape (Cf. FIG. 7), a cruciform shape (Cf. FIG. 8), a numericcharacter 1 shape (FIG. 9), a T shape extending along the lengthwisedirection of the wired circuit board 1 (Cf. FIG. 10), a T shapeextending along the widthwise direction of the wired circuit board 1(Cf. FIG. 11), an L shape (Cf. FIG. 12), and a circular shape (Cf. FIG.13). The planar shape may be properly selected depending on intendedpurposes and applications.

Preferably, the criterion marks 8 have a planar shape including a linearportion through which the reference line BL indicated by the dotted linecan be clearly identified between the opposing criterion marks 8 in thewidthwise direction, like the respective criterion marks 8 shown inFIGS. 7-12.

The criterion marks 8 shown in FIGS. 7-12 have a lengthwise dimension L1of 15-150 μm, or preferably 30-80 μm, and a widthwise dimension L2 of15-150 μm, or preferably 30-80 μm.

Although in the embodiment illustrated above, the criterion marks 8 areformed from the same metal as that of the conductive pattern 3 at thesame time that the conductive pattern 3 is formed, as long as thecriterion marks 8 can serve as the criterion on the presence or absenceof the inhibitory portion 23 for the microscopic observation orexamination, no particularly limitation is imposed on the formation ofthe criterion marks 8. For example, the criterion marks 8 may be formedby forming cavities or through holes in the insulating base layer 2exposed from the opening 7 of the insulating cover layer 4 by mold orlaser processing.

EXAMPLE

While in the following, the present invention will be described infurther detail with reference to Examples, the present invention is notlimited thereto.

Example 1

Thousand wired circuit boards were produced in the following sequences.

An etching resist of 10 μm thick was formed on a copper clad laminate(two-layer base material) formed by laminating a copper foil of 18 μmthick on the insulating base layer of polyimide resin of 25 μm thick inthe form of a pattern corresponding to the conductive pattern and thecriterion marks by exposing a dry film photoresist to light anddeveloping it.

Then, the copper foil exposed from the etching resist was etched usingaqueous ferric chloride, whereby the conductive pattern including theterminal portions and the criterion marks (of a square, 50 μm on a side)were formed simultaneously (Cf. FIG. 2( b)).

Then, after the etching resist was stripped, solder resist was coatedover the insulating base layer including the conductive pattern, to formthe opening corresponding to the terminal portions by photolithography.Thereafter, the solder resist was cured to thereby form the insulatingcover layer of 10 μm thick (Cf. FIG. 2( c)).

Then, the presence or absence of an inhibitory portion was determinedwith reference to the criterion marks exposed from the opening of theinsulating cover layer by examination under an optical microscope.

When the insulating cover layer was formed from the solder resist, thesolder resist started to flow into between the lines of wire at theterminal portions due to the capillary phenomenon, going inwardly of theopening in the lengthwise direction of the lines of wire. When theflowing solder resist went beyond the criterion marks, a portion of thesolder resist extending inwardly beyond the criterion marks wasdetermined as the inhibitory portion.

When the inhibitory portion was present, the wired circuit board havingsuch an inhibitory portion was dealt with as defective goods. On theother hand, when the inhibitory portion was absent, the wired circuitboard having such an inhibitory portion was dealt with as confirminggoods, so that an electronic component was mounted on the wired circuitboard.

Example 2

Thousand wired circuit boards were produced in the following sequences.

An etching resist of 10 μm thick was formed on a copper clad laminate(two-layer base material) formed by laminating a copper foil of 18 μmthick on the insulating base layer of polyimide resin of 25 μm thick inthe form of a pattern corresponding to the conductive pattern byexposing a dry film photoresist to light and developing it.

Then, the copper foil exposed from the etching resist was etched usingaqueous ferric chloride, whereby the conductive pattern including theterminal portions was formed.

Then, after the etching resist was stripped, the criterion marks ofcircular through holes having a diameter of 50 μm were formed in theinsulating base layer at the both widthwise outer sides further awayfrom the both widthwise outermost sides of the lines of wire at theterminal portions by using ultraviolet laser.

Then, solder resist was coated over the insulating base layer includingthe conductive pattern, to form the opening corresponding to theterminal portions by photolithography. Thereafter, the solder resist wascured to thereby form the insulating cover layer of 10 μm thick.

Then, the presence or absence of an inhibitory portion was determinedwith reference to the criterion marks exposed from the opening of theinsulating cover layer by examination under an optical microscope.

When the insulating cover layer was formed from the solder resist, thesolder resist started to flow into between the lines of wire at theterminal portions due to the capillary phenomenon, going inwardly of theopening in the lengthwise direction of the lines of wire. When theflowing solder resist went beyond the criterion marks, a portion of thesolder resist extending inwardly beyond the criterion marks wasdetermined as the inhibitory portion.

When the inhibitory portion was present, the wired circuit board havingsuch an inhibitory portion was dealt with as defective goods. On theother hand, when no inhibitory portion was present, the wired circuitboard having such an inhibitory portion was dealt with as confirminggoods, so that an electronic component was mounted on the wired circuitboard.

While the illustrative embodiments of the present invention are providedin the above description, such is for illustrative purpose only and itis not to be construed restrictively. Modification and variation of thepresent invention that will be obvious to those skilled in the art is tobe covered by the following claims.

1. A wired circuit board comprising: an insulating base layer; aconductive pattern formed on the insulating base layer, the conductivepattern including a plurality of lines of wire extending along alengthwise direction of the wired circuit board; an insulating coverlayer formed on the insulating base layer to cover the conductivepattern; terminal portions coupled to the conductive pattern, theterminal portions being provided to connect with external terminals ofan external component; an opening formed in the insulating cover layerto expose the terminal portions and to provide a mounting area for theexternal component; an inhibitory region defined between an edge of theopening and a corresponding edge of the mounting area for the externalcomponent, the inhibitory region including the terminal portions thereinand not including the insulating cover layer between the terminalportions; and criterion marks provided on the insulating base layerbetween the edge of the opening and the corresponding edge of themounting area of the external component to identify boundaries of theinhibitory region, the criterion marks being exposed from the openingand identifying the boundaries for enabling a determination of whetherthe insulating cover layer extends into the inhibitory region, whereinthe criterion marks are arranged so as to interpose the lines of wireand formed in a triangular shape, one side thereof is arranged along adirection orthogonal to a longitudinal direction of the lines of wire,and a reference line for the determination is drawn with a straight linetangent to the one side of the criterion marks.